We propose to study the acute effects of the increasingly popular designer drug gamma-hydroxy butyric acid (GHB) on neurons in the ventral tegmental area (mesolimbic dopamine system). The actions of GHB are mediated through G protein-coupled receptors (GPCRs)of the GABAB type, activating downstream effectors, such as G protein-gated inwardly rectifying potassium (Kir3 or GIRK) channels. We hypothesize that specific combinations of GIRK channels play a primary role in mediating acute rewarding effects of GABAg receptor agonists on mesolimbic dopamine system. We will (1) elucidate the role of regulator of G-protein signaling (RGS) proteins in modulating the coupling efficiency of GABAB receptors, (2) asses the role of GIRK channel subunits (GIRK1, GIRK2, and GIRK3) on setting the coupling efficiency of GABAB receptors in dopamine and GABA neurons of the VTA, and (3) determine single-channel properties and rules of assembly of heteromeric GIRK channels in the VTA. We will use a two-pronged approach [unreadable] a systems level approach involving patch-clamp recordings and two-photon imaging in acute brain slices from wild-type, GIRK- deficient, and transgenic mice; and a cellular approach, involving patch-clamp recordings and advanced imaging techniques from GIRK channels expressed in heterologous cells and in cultured neurons of the VTA. Together, these studies will reveal the cellular and molecular events underlying GIRK channel assembly and coupling to GABAs receptors in the brain, as well as elucidate the role of GIRK channels in determining the efficacy of GHB and related drugs in the brain. Public health relevance. Drug abuse is a USand world-wide problem affecting millions of people. Drugs of abuse impart strong sensations of reward, which may lead to repetitive drug administration, dependence and addiction. Addiction is characterized by relapse in response to uncontrollable cravings. The initial rewarding effects as well as the cravings are associated with the activation of the mesolimbic dopamine system. The abuse of GHB has increased dramatically over the last few years. By unraveling the role of GIRK channels in mediating GHB actions, we may reveal targets for new drugs that either directly activate these channels or alter the coupling efficiency to GPCRs. Such an approach may establish GIRK channels as formidable drug targets for treating addiction.